ANSWER:
It is your right to demand a separate accommodation where you don’t need to see any of them!
However, you should weigh the pros and cons as if you know he can’t afford that, you shouldn’t embarrass yourself.
It is not logical to expect him to disrespect his mother or scold her for a misunderstanding. It is best that you deal with them as you deal with any bullies who try to get a negative remark from you. Simply ignore them and smile in their face. Never argue and never defend yourself no matter what they say or do.
This would kill them softly and would turn the tables over their heads and make you win in the eyes of others for being polite and peaceful.